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How quickly are they adding new content to the site and are they using Twitter/FB/Pinterest/G+ as a resource for getting their URLs crawled more frequently? That's worth checking out.

Using the keyword tactic is a bad idea. Comments are meant to be personalized so using a fake name or a keyword is not recommended. UX still factors into SEO so you could be harming your site and the site you're commenting on by doing that.

That's amazing! What a leap of faith! My recommendation/advice is to read, read, read. Get your hands on books on UX. Read up on how to perform a content audit. Read through as much about SEO as possible. SEO has been my passion for nearly a decade and I'm still learning.

Also remember not to take yourself too seriously. You WILL have clients that think they know everything. You WILL have clients that make you want to rip your hair out. It's normal. Pick your clients carefully. You're the expert, not them. And never call yourself a 'guru'.

Great question! You can always do a site search on Google or use Screaming Frog (best recommendation). You can use Screaming Frog and and keep an eye out for new pages.

Doing it manually can be time consuming but you can always use their content as a basis for new content ideas within your client's site.

Targeted backlinks utilizing keywords in place of your actual name are not recommended. Google will still recognize the backlink - it just won't have targeted anchor text. If you use targeted anchor text, Google may see the backlink as spam, this is why it's not recommended.

Forums may be a better choice for you, but I would still use caution there.